This application is aimed at characterizing some of structural-functional features of Annexin XII from the Hydra vulgaris. Based on previous results, the investigator proposes new models for annexin-mediated membrane aggregation/fusion and channel activity. Studies will also examine the mechanism of interaction between annexin XII and lipid bilayers. The investigator notes that elucidation of the structure of membrane-bound annexin will provide a solid foundation for evaluating their proposed biological functions. Four Specific Aims will be pursued: (1) to determine the structure of annexin XII bound to phospholipid bilayers; (2) to investigate the molecular mechanisms of annexin-induced ion flux across bilayers; (3) to determine whether the annexin XII hexamers mediate vesicle aggregation/fusion; and (4) to determine the structural/ functional consequence of annexin XII phosphorylation